Non-contacting surface measurement gauges are available which compare the relative quality of a test surface with respect to a known surface of the same type. Such gauges are offered commercially by Measurement Arts, Inc. of Providence, R.I. under the name Explorer I Surface Quality Measurement System. While that system has been accepted in the industry, it does not directly measure roughness in micrometers, it is undesirably sensitive to surface reflectivity, and it is limited to measuring surface quality at a right angle to the lay or to the direction of surface irregularities such as machining grooves. Another deficiency is that the measuring head thereof is too large so that it can't measure in tight spots. Specifically, that system cannot measure the cylindrical surface finish of a crankshaft bearing at the desired location relatively close to a crankshaft shoulder, for example.
Other surface quality gauges are known, such as those employing laser beams, which are excessively complex and fragile in construction. As far as is known, all known gauges must be recalibrated for each change in surface character, lay and/or reflectivity. Such recalibration has heretofore been too time-consuming and costly.
Accordingly, what is desired is a relatively inexpensive, compact and simple gauge that can provide a direct reading of the surface roughness of an article in micrometers or microinches independent of the direction of lay of the grinding or machining marks with but minor recalibration, and independent of the reflectivity of the surface. Another desired feature is to provide a gauge which can easily be recalibrated for measuring articles of different surface contour.
The present invention is directed to overcoming one or more of the problems as set forth above.